This disclosure relates to rack bar haulage systems and the means by which the rack bars are secured and retained to armor face conveyors, in particular, though not necessarily exclusively, for underground longwall mining.
Longwall conveyors normally operate with a powered coal-cutting machine, a shearer that is mounted onto the face conveyor. The shearer hauls itself along the face conveyor in both directions by means of a haulage system. A rack bar haulage systems comprise a series of rack bars pinned to support brackets, called clogs, welded to the individual armor face conveyor elements, the line pan. The shearer engages with the racks via a shoe that permits free movement in the direction of shearer travel only. The shoe also houses a drive sprocket that engages the gear teeth to provide the required haulage load to cut the mined material. The shearer drive gear wheel meshes with uniformly spaced horizontal teeth extending between two spaced apart cheek plates to form the rack bar.
All rack systems must withstand shearer haulage forces in various directions and their retention methods must cope with the tendency of the shearer shoe to bulldoze material in front of it as it passes along the conveyor.
In conventional longwall mining, as illustrated in FIGS. 1-2 taken from Lanfermann et al U.S. Pat. No. 4,155,600, a drum cutter mining machine 1 is traversed along a face conveyor 2 by means of a driving wheel 3 secured to a longwall shearer 4. The driving wheel 3 meshes with a gearwheel or drive sprocket 5 that is rotatably supported on the machine frame 6 forming part of the drum cutter mining machine. The teeth of the drive sprocket 5 mesh with rack gear teeth of a rack bar or device 7.
As illustrated in FIG. 2, the face conveyor 2 is made up of a plurality of conveyor pan sections or line pans 9 joined together end-to-end by connecting elements 8. By means of these connecting elements, the conveyor pan sections are maintained movable with respect to each other so that the conveyor pan sections are adaptable to characteristics of the mine floor. The individual conveyor pan sections are connected together by the connecting elements 8 to provide not only limited mobility with respect to each other in the horizontal direction of the conveyor 2, but also to provide vertical or horizontal angling of one conveyor pan section with respect to another when set on the mine floor. The rack device 7 that is mounted onto the face conveyor 2 undergoes the same horizontal motions as the conveyor pan sections. When the face conveyor is shifted, the rack device also undergoes the same vertical angular motions which the conveyor pan sections undergo particularly when it is desired to work undulating portions of a mine seam. The rack device 7 includes a plurality of elongated rack bars consisting of movable rack bars 7a and immovable rack bars 7b. Holders or clogs 10 that are directly or indirectly connected to the face conveyor 2 support all the rack bars. Connecting bolts 11 are used to join the individual rack bars to the clogs 10.
The movable and immovable rack bars 7a and 7b, respectively, of the rack device 7 are provided at both ends of each segment with a nose-shaped extension 12 which projects downwardly. This extension includes a bore for accommodating a connecting bolt 11 forming a pivot shaft. As shown in FIG. 1, the movable rack bars 7a bridge a joint A between the conveyor pan sections. The movable rack bars 7a are mounted onto the same two holders 10 which are used to mount one end of adjacent immovable rack bars 7b. These immovable rack bars are each entirely disposed to extend along a single conveyor pan section. Thus, two rack clogs 10 are secured at spaced-apart locations to a conveyor pan section. Each immovable rack bar 7b is secured by connecting bolts or pins 11 at its opposite ends to the two rack holders which additionally support the adjacent ends of movable rack bars.
Each of the clogs 10 is provided with a slot 13 located on one-half of the holders that is nearest the joint between the conveyor pan sections. The slots 13 in the clogs 10 extend in a direction corresponding to the longitudinal orientation of the face conveyor. The connecting pins 11 extend through the slots and provide the associated movable rack bar 7a with adequate mobility with respect to the face conveyor. The immovable rack bars 7b are fixed with respect to the face conveyor 2 by the connecting bolts 11 which retain these rack bars by extending through bores 13′ formed in the remaining half of the holders 10. Each bore 13′ corresponds to the diameter of the pin 11.
Thus, it is common to have two rack bars 7 per line pan 9. One rack bar 7b is fixed in the center of the line pan 9, and the second rack bar 7a spans the joint between adjacent line pans 9. Relative articulation between line pans during the mining process can cause the inter-pan gap to vary considerably and this could cause problems as the shearer drive sprocket 5 moves from the fixed rack bar 7b to the inter-pan rack bar 7a, if the inter-pan rack bar is firmly pinned to either adjacent pan. The common solution is for the inter-pan rack bar pins 11 to be retained in slots 13 in the clogs 10 rather than holes. In this manner, the error in tooth pitch between adjacent rack bars is halved and is kinder to the shearer sprocket 5, but causes added difficulty with pin retention, as the pin 11 must be allowed to move along the slot 13.
More particularly, as shown in FIGS. 3, 4 and 5, the longwall line pans 9 include a goaf side fabrication or shield plate 14. The shield plate 14 is located adjacent the rack bar haulage system. In order to secure the rack bar 7 to the clog 10, the pin 11 is inserted into the clog 10 through an opening 15 in the shield plate 14.
The clog 10 has a width corresponding to the width of the nose-shaped extension 12, and the clog 10 defines a cavity for engaging and providing support for the rack bar 7 by receiving the nose-shaped extension 12, the cavity being defined by two spaced apart bracket sidewalls 16, and end walls 17 connecting the sidewalls 16. The clog 10 also has openings 18 through the sidewalls 16, the pin 11 being insertable through one sidewall opening 18 and being received in the other sidewall opening 18.
The pin has a head 19 that is larger than the opening through the sidewall of the clog 10, so the pin 11 cannot pass through the clog 10. In order to retain the pin 11 within the clog 10, a retainer plate 20 is dropped into the area between the head of the pin 11 and the shield plate 14. The retainer plate 20 prevents the pin 11 from coming out of the clog 10.
Thus, as shown in FIGS. 3-5, the conventional rack bars 7 are retained in the clogs 10 by the headed pins 11 that can only be assembled through the opening 15 in the goaf side shield plate 14. The headed pins 11 are themselves retained by the retainer plates 20 that locate in lugs 21 welded to the goaf side shield plate 14. The retainer plates 20 are kept in place by gravity alone, but can be made more secure with another fastener, such as a bolt or a spring pin.
The primary role of the clog 10 is to provide fixing points on the line pans 7 for the semi-flexible rack bar system along which the shearer hauls itself in order to cut material from the seam. The nature of the system is that rack bars 7 are easily replaced if damaged, but the clogs 10 cannot be repaired in a hazardous environment, as the required cutting and welding is prohibited. Hence there is a need for a strong, reliable, simple rack-clog retention assembly.